"""
Gamma and related functions
"""
from sage.symbolic.function import GinacFunction, BuiltinFunction
from sage.symbolic.expression import register_symbol, symbol_table
from sage.structure.all import parent as s_parent
from sage.rings.complex_mpfr import ComplexField
from sage.rings.rational import Rational
from sage.functions.exp_integral import Ei
from sage.libs.mpmath import utils as mpmath_utils
from .log import exp
from .other import sqrt
from sage.symbolic.constants import pi


class Function_gamma(GinacFunction):
    def __init__(self):
        r"""
        The Gamma function.  This is defined by

        .. MATH::

            \Gamma(z) = \int_0^\infty t^{z-1}e^{-t} dt

        for complex input `z` with real part greater than zero, and by
        analytic continuation on the rest of the complex plane (except
        for negative integers, which are poles).

        It is computed by various libraries within Sage, depending on
        the input type.

        EXAMPLES::

            sage: from sage.functions.gamma import gamma1
            sage: gamma1(CDF(0.5,14))
            -4.0537030780372815e-10 - 5.773299834553605e-10*I
            sage: gamma1(CDF(I))
            -0.15494982830181067 - 0.49801566811835607*I

        Recall that `\Gamma(n)` is `n-1` factorial::

            sage: gamma1(11) == factorial(10)
            True
            sage: gamma1(6)
            120
            sage: gamma1(1/2)
            sqrt(pi)
            sage: gamma1(-1)
            Infinity
            sage: gamma1(I)
            gamma(I)
            sage: gamma1(x/2)(x=5)
            3/4*sqrt(pi)

            sage: gamma1(float(6))  # For ARM: rel tol 3e-16
            120.0
            sage: gamma(6.)
            120.000000000000
            sage: gamma1(x)
            gamma(x)

        ::

            sage: gamma1(pi)
            gamma(pi)
            sage: gamma1(i)
            gamma(I)
            sage: gamma1(i).n()
            -0.154949828301811 - 0.498015668118356*I
            sage: gamma1(int(5))
            24

        ::

            sage: conjugate(gamma(x))
            gamma(conjugate(x))

        ::

            sage: plot(gamma1(x),(x,1,5))
            Graphics object consisting of 1 graphics primitive

        We are also able to compute the Laurent expansion of the
        Gamma function (as well as of functions containing
        the Gamma function)::

            sage: gamma(x).series(x==0, 2)
            1*x^(-1) + (-euler_gamma)
            + (1/2*euler_gamma^2 + 1/12*pi^2)*x + Order(x^2)
            sage: (gamma(x)^2).series(x==0, 1)
            1*x^(-2) + (-2*euler_gamma)*x^(-1)
            + (2*euler_gamma^2 + 1/6*pi^2) + Order(x)

        To prevent automatic evaluation use the ``hold`` argument::

            sage: gamma1(1/2,hold=True)
            gamma(1/2)

        To then evaluate again, we currently must use Maxima via
        :meth:`sage.symbolic.expression.Expression.simplify`::

            sage: gamma1(1/2,hold=True).simplify()
            sqrt(pi)

        TESTS:

            sage: gamma(x)._sympy_()
            gamma(x)

        We verify that we can convert this function to Maxima and
        convert back to Sage::

            sage: z = var('z')
            sage: maxima(gamma1(z)).sage()
            gamma(z)
            sage: latex(gamma1(z))
            \Gamma\left(z\right)

        Test that :trac:`5556` is fixed::

            sage: gamma1(3/4)
            gamma(3/4)

            sage: gamma1(3/4).n(100)
            1.2254167024651776451290983034

        Check that negative integer input works::

            sage: (-1).gamma()
            Infinity
            sage: (-1.).gamma()
            NaN
            sage: CC(-1).gamma()
            Infinity
            sage: RDF(-1).gamma()
            NaN
            sage: CDF(-1).gamma()
            Infinity

        Check if :trac:`8297` is fixed::

            sage: latex(gamma(1/4))
            \Gamma\left(\frac{1}{4}\right)

        Test pickling::

            sage: loads(dumps(gamma(x)))
            gamma(x)

        Check that the implementations roughly agrees (note there might be
        difference of several ulp on more complicated entries)::

            sage: import mpmath
            sage: float(gamma(10.)) == gamma(10.r) == float(gamma(mpmath.mpf(10)))
            True
            sage: float(gamma(8.5)) == gamma(8.5r) == float(gamma(mpmath.mpf(8.5)))
            True

        Check that ``QQbar`` half integers work with the ``pi`` formula::

            sage: gamma(QQbar(1/2))
            sqrt(pi)
            sage: gamma(QQbar(-9/2))
            -32/945*sqrt(pi)

        .. SEEALSO::

            :meth:`gamma`
        """
        GinacFunction.__init__(self, 'gamma', latex_name=r"\Gamma",
                               ginac_name='gamma',
                               conversions={'mathematica':'Gamma',
                                            'maple':'GAMMA',
                                            'sympy':'gamma',
                                            'fricas':'Gamma',
                                            'giac':'Gamma'})

gamma1 = Function_gamma()


class Function_log_gamma(GinacFunction):
    def __init__(self):
        r"""
        The principal branch of the log gamma function. Note that for
        `x < 0`, ``log(gamma(x))`` is not, in general, equal to
        ``log_gamma(x)``.

        It is computed by the ``log_gamma`` function for the number type,
        or by ``lgamma`` in Ginac, failing that.

        Gamma is defined for complex input `z` with real part greater
        than zero, and by analytic continuation on the rest of the
        complex plane (except for negative integers, which are poles).

        EXAMPLES:

        Numerical evaluation happens when appropriate, to the
        appropriate accuracy (see :trac:`10072`)::

            sage: log_gamma(6)
            log(120)
            sage: log_gamma(6.)
            4.78749174278205
            sage: log_gamma(6).n()
            4.78749174278205
            sage: log_gamma(RealField(100)(6))
            4.7874917427820459942477009345
            sage: log_gamma(2.4 + I)
            -0.0308566579348816 + 0.693427705955790*I
            sage: log_gamma(-3.1)
            0.400311696703985 - 12.5663706143592*I
            sage: log_gamma(-1.1) == log(gamma(-1.1))
            False

        Symbolic input works (see :trac:`10075`)::

            sage: log_gamma(3*x)
            log_gamma(3*x)
            sage: log_gamma(3 + I)
            log_gamma(I + 3)
            sage: log_gamma(3 + I + x)
            log_gamma(x + I + 3)

        Check that :trac:`12521` is fixed::

            sage: log_gamma(-2.1)
            1.53171380819509 - 9.42477796076938*I
            sage: log_gamma(CC(-2.1))
            1.53171380819509 - 9.42477796076938*I
            sage: log_gamma(-21/10).n()
            1.53171380819509 - 9.42477796076938*I
            sage: exp(log_gamma(-1.3) + log_gamma(-0.4) -
            ....:     log_gamma(-1.3 - 0.4)).real_part()  # beta(-1.3, -0.4)
            -4.92909641669610

        In order to prevent evaluation, use the ``hold`` argument;
        to evaluate a held expression, use the ``n()`` numerical
        evaluation method::

            sage: log_gamma(SR(5), hold=True)
            log_gamma(5)
            sage: log_gamma(SR(5), hold=True).n()
            3.17805383034795

        TESTS::

            sage: log_gamma(-2.1 + I)
            -1.90373724496982 - 7.18482377077183*I
            sage: log_gamma(pari(6))
            4.78749174278205
            sage: log_gamma(x)._sympy_()
            loggamma(x)
            sage: log_gamma(CC(6))
            4.78749174278205
            sage: log_gamma(CC(-2.5))
            -0.0562437164976741 - 9.42477796076938*I
            sage: log_gamma(RDF(-2.5))
            -0.056243716497674054 - 9.42477796076938*I
            sage: log_gamma(CDF(-2.5))
            -0.056243716497674054 - 9.42477796076938*I
            sage: log_gamma(float(-2.5))
            (-0.056243716497674054-9.42477796076938j)
            sage: log_gamma(complex(-2.5))
            (-0.056243716497674054-9.42477796076938j)

        ``conjugate(log_gamma(x)) == log_gamma(conjugate(x))`` unless on the
        branch cut, which runs along the negative real axis.::

            sage: conjugate(log_gamma(x))
            conjugate(log_gamma(x))
            sage: var('y', domain='positive')
            y
            sage: conjugate(log_gamma(y))
            log_gamma(y)
            sage: conjugate(log_gamma(y + I))
            conjugate(log_gamma(y + I))
            sage: log_gamma(-2)
            +Infinity
            sage: conjugate(log_gamma(-2))
            +Infinity
        """
        GinacFunction.__init__(self, "log_gamma", latex_name=r'\log\Gamma',
                               conversions=dict(mathematica='LogGamma',
                                                maxima='log_gamma',
                                                sympy='loggamma',
                                                fricas='logGamma'))


log_gamma = Function_log_gamma()


class Function_gamma_inc(BuiltinFunction):
    def __init__(self):
        r"""
        The upper incomplete gamma function.

        It is defined by the integral

        .. MATH::

            \Gamma(a,z)=\int_z^\infty t^{a-1}e^{-t}\,\mathrm{d}t

        EXAMPLES::

            sage: gamma_inc(CDF(0,1), 3)
            0.0032085749933691158 + 0.012406185811871568*I
            sage: gamma_inc(RDF(1), 3)
            0.049787068367863944
            sage: gamma_inc(3,2)
            gamma(3, 2)
            sage: gamma_inc(x,0)
            gamma(x)
            sage: latex(gamma_inc(3,2))
            \Gamma\left(3, 2\right)
            sage: loads(dumps((gamma_inc(3,2))))
            gamma(3, 2)
            sage: i = ComplexField(30).0; gamma_inc(2, 1 + i)
            0.70709210 - 0.42035364*I
            sage: gamma_inc(2., 5)
            0.0404276819945128
            sage: x,y=var('x,y')
            sage: gamma_inc(x,y).diff(x)
            diff(gamma(x, y), x)
            sage: (gamma_inc(x,x+1).diff(x)).simplify()
            -(x + 1)^(x - 1)*e^(-x - 1) + D[0](gamma)(x, x + 1)

        TESTS:

        Check that :trac:`21407` is fixed::

            sage: gamma(-1,5)._sympy_()
            expint(2, 5)/5
            sage: gamma(-3/2,5)._sympy_()
            -6*sqrt(5)*exp(-5)/25 + 4*sqrt(pi)*erfc(sqrt(5))/3

        Check that :trac:`25597` is fixed::

            sage: gamma(-1,5)._fricas_()                                        # optional - fricas
            Gamma(- 1,5)

            sage: var('t')                                                      # optional - fricas
            t
            sage: integrate(-exp(-x)*x^(t-1), x, algorithm="fricas")            # optional - fricas
            gamma(t, x)

        .. SEEALSO::

            :meth:`gamma`
        """
        BuiltinFunction.__init__(self, "gamma", nargs=2, latex_name=r"\Gamma",
                conversions={'maxima':'gamma_incomplete', 'mathematica':'Gamma',
                             'maple':'GAMMA', 'sympy':'uppergamma', 'fricas':'Gamma',
                             'giac':'ugamma'})

    def _method_arguments(self, x, y):
        r"""
        TESTS::

            sage: b = RBF(1, 1e-10)
            sage: gamma(b) # abs tol 1e-9
            [1.0000000000 +/- 5.78e-11]
            sage: gamma(CBF(b)) # abs tol 1e-9
            [1.0000000000 +/- 5.78e-11]
            sage: gamma(CBF(b), 4) # abs tol 2e-9
            [0.018315639 +/- 9.00e-10]
            sage: gamma(CBF(1), b)
            [0.3678794412 +/- 6.54e-11]
        """
        return [x, y]

    def _eval_(self, x, y):
        """
        EXAMPLES::

            sage: gamma_inc(2.,0)
            1.00000000000000
            sage: gamma_inc(2,0)
            1
            sage: gamma_inc(1/2,2)
            -sqrt(pi)*(erf(sqrt(2)) - 1)
            sage: gamma_inc(1/2,1)
            -sqrt(pi)*(erf(1) - 1)
            sage: gamma_inc(1/2,0)
            sqrt(pi)
            sage: gamma_inc(x,0)
            gamma(x)
            sage: gamma_inc(1,2)
            e^(-2)
            sage: gamma_inc(0,2)
            -Ei(-2)
        """
        if y == 0:
            return gamma(x)
        if x == 1:
            return exp(-y)
        if x == 0:
            return -Ei(-y)
        if x == Rational((1, 2)):  # only for x>0
            from sage.functions.error import erf
            return sqrt(pi) * (1 - erf(sqrt(y)))
        return None

    def _evalf_(self, x, y, parent=None, algorithm='pari'):
        """
        EXAMPLES::

            sage: gamma_inc(0,2)
            -Ei(-2)
            sage: gamma_inc(0,2.)
            0.0489005107080611
            sage: gamma_inc(0,2).n(algorithm='pari')
            0.0489005107080611
            sage: gamma_inc(0,2).n(200)
            0.048900510708061119567239835228...
            sage: gamma_inc(3,2).n()
            1.35335283236613

        TESTS:

        Check that :trac:`7099` is fixed::

            sage: R = RealField(1024)
            sage: gamma(R(9), R(10^-3))  # rel tol 1e-308
            40319.99999999999999999999999999988898884344822911869926361916294165058203634104838326009191542490601781777105678829520585311300510347676330951251563007679436243294653538925717144381702105700908686088851362675381239820118402497959018315224423868693918493033078310647199219674433536605771315869983788442389633
            sage: numerical_approx(gamma(9, 10^(-3)) - gamma(9), digits=40)  # abs tol 1e-36
            -1.110111598370794007949063502542063148294e-28

        Check that :trac:`17328` is fixed::

            sage: gamma_inc(float(-1), float(-1))
            (-0.8231640121031085+3.141592653589793j)
            sage: gamma_inc(RR(-1), RR(-1))
            -0.823164012103109 + 3.14159265358979*I
            sage: gamma_inc(-1, float(-log(3))) - gamma_inc(-1, float(-log(2)))  # abs tol 1e-15
            (1.2730972164471142+0j)

        Check that :trac:`17130` is fixed::

            sage: r = gamma_inc(float(0), float(1)); r
            0.21938393439552029
            sage: type(r)
            <... 'float'>
        """
        R = parent or s_parent(x)
        # C is the complex version of R
        # prec is the precision of R
        if R is float:
            prec = 53
            C = complex
        else:
            try:
                prec = R.precision()
            except AttributeError:
                prec = 53
            try:
                C = R.complex_field()
            except AttributeError:
                C = R

        if algorithm == 'pari':
            v = ComplexField(prec)(x).gamma_inc(y)
        else:
            import mpmath
            v = ComplexField(prec)(mpmath_utils.call(mpmath.gammainc, x, y, parent=R))
        if v.is_real():
            return R(v)
        else:
            return C(v)

# synonym.
gamma_inc = Function_gamma_inc()


class Function_gamma_inc_lower(BuiltinFunction):
    def __init__(self):
        r"""
        The lower incomplete gamma function.

        It is defined by the integral

        .. MATH::

            \Gamma(a,z)=\int_0^z t^{a-1}e^{-t}\,\mathrm{d}t

        EXAMPLES::

            sage: gamma_inc_lower(CDF(0,1), 3)
            -0.1581584032951798 - 0.5104218539302277*I
            sage: gamma_inc_lower(RDF(1), 3)
            0.950212931632136
            sage: gamma_inc_lower(3, 2, hold=True)
            gamma_inc_lower(3, 2)
            sage: gamma_inc_lower(3, 2)
            -10*e^(-2) + 2
            sage: gamma_inc_lower(x, 0)
            0
            sage: latex(gamma_inc_lower(x, x))
            \gamma\left(x, x\right)
            sage: loads(dumps((gamma_inc_lower(x, x))))
            gamma_inc_lower(x, x)
            sage: i = ComplexField(30).0; gamma_inc_lower(2, 1 + i)
            0.29290790 + 0.42035364*I
            sage: gamma_inc_lower(2., 5)
            0.959572318005487

        Interfaces to other software::

            sage: gamma_inc_lower(x,x)._sympy_()
            lowergamma(x, x)
            sage: maxima(gamma_inc_lower(x,x))
            gamma_incomplete_lower(_SAGE_VAR_x,_SAGE_VAR_x)

    .. SEEALSO::

        :class:`Function_gamma_inc`
        """
        BuiltinFunction.__init__(self, "gamma_inc_lower", nargs=2, latex_name=r"\gamma",
                conversions={'maxima':'gamma_incomplete_lower',
                    'maple':'GAMMA', 'sympy':'lowergamma', 'giac':'igamma'})

    def _eval_(self, x, y):
        """
        EXAMPLES::

            sage: gamma_inc_lower(2.,0)
            0.000000000000000
            sage: gamma_inc_lower(2,0)
            0
            sage: gamma_inc_lower(1/2,2)
            sqrt(pi)*erf(sqrt(2))
            sage: gamma_inc_lower(1/2,1)
            sqrt(pi)*erf(1)
            sage: gamma_inc_lower(1/2,0)
            0
            sage: gamma_inc_lower(x,0)
            0
            sage: gamma_inc_lower(1,2)
            -e^(-2) + 1
            sage: gamma_inc_lower(0,2)
            +Infinity
            sage: gamma_inc_lower(2,377/79)
            -456/79*e^(-377/79) + 1
            sage: gamma_inc_lower(3,x)
            -(x^2 + 2*x + 2)*e^(-x) + 2
            sage: gamma_inc_lower(9/2,37/7)
            -1/38416*sqrt(pi)*(1672946*sqrt(259)*e^(-37/7)/sqrt(pi) - 252105*erf(1/7*sqrt(259)))
        """
        if y == 0:
            return 0
        if x == 0:
            from sage.rings.infinity import Infinity
            return Infinity
        elif x == 1:
            return 1 - exp(-y)
        elif (2 * x).is_integer():
            return self(x, y, hold=True)._sympy_()
        else:
            return None

    def _evalf_(self, x, y, parent=None, algorithm='mpmath'):
        """
        EXAMPLES::

            sage: gamma_inc_lower(3,2.)
            0.646647167633873
            sage: gamma_inc_lower(3,2).n(200)
            0.646647167633873081060005050275155...
            sage: gamma_inc_lower(0,2.)
            +infinity
        """
        R = parent or s_parent(x)
        # C is the complex version of R
        # prec is the precision of R
        if R is float:
            prec = 53
            C = complex
        else:
            try:
                prec = R.precision()
            except AttributeError:
                prec = 53
            try:
                C = R.complex_field()
            except AttributeError:
                C = R
        if algorithm == 'pari':
            Cx = ComplexField(prec)(x)
            v = Cx.gamma() - Cx.gamma_inc(y)
        else:
            import mpmath
            v = ComplexField(prec)(mpmath_utils.call(mpmath.gammainc, x, 0, y, parent=R))
        return R(v) if v.is_real() else C(v)

    def _derivative_(self, x, y, diff_param=None):
        """
        EXAMPLES::

            sage: x,y = var('x,y')
            sage: gamma_inc_lower(x,y).diff(y)
            y^(x - 1)*e^(-y)
            sage: gamma_inc_lower(x,y).diff(x)
            Traceback (most recent call last):
            ...
            NotImplementedError: cannot differentiate gamma_inc_lower in the first parameter
        """
        if diff_param == 0:
            raise NotImplementedError("cannot differentiate gamma_inc_lower in the"
                                      " first parameter")
        else:
            return exp(-y) * y**(x - 1)

    def _mathematica_init_evaled_(self, *args):
        r"""
        EXAMPLES::

            sage: gamma_inc_lower(4/3, 1)._mathematica_()  # indirect doctest, optional - mathematica
            Gamma[4/3, 0, 1]
        """
        args_mathematica = []
        for a in args:
            if isinstance(a, str):
                args_mathematica.append(a)
            elif hasattr(a, '_mathematica_init_'):
                args_mathematica.append(a._mathematica_init_())
            else:
                args_mathematica.append(str(a))
        x, z = args_mathematica
        return "Gamma[%s,0,%s]" % (x, z)

# synonym.
gamma_inc_lower = Function_gamma_inc_lower()


def gamma(a, *args, **kwds):
    r"""
    Gamma and upper incomplete gamma functions in one symbol.

    Recall that `\Gamma(n)` is `n-1` factorial::

        sage: gamma(11) == factorial(10)
        True
        sage: gamma(6)
        120
        sage: gamma(1/2)
        sqrt(pi)
        sage: gamma(-4/3)
        gamma(-4/3)
        sage: gamma(-1)
        Infinity
        sage: gamma(0)
        Infinity

    ::

        sage: gamma_inc(3,2)
        gamma(3, 2)
        sage: gamma_inc(x,0)
        gamma(x)

    ::

        sage: gamma(5, hold=True)
        gamma(5)
        sage: gamma(x, 0, hold=True)
        gamma(x, 0)

    ::

        sage: gamma(CDF(I))
        -0.15494982830181067 - 0.49801566811835607*I
        sage: gamma(CDF(0.5,14))
        -4.0537030780372815e-10 - 5.773299834553605e-10*I

    Use ``numerical_approx`` to get higher precision from
    symbolic expressions::

        sage: gamma(pi).n(100)
        2.2880377953400324179595889091
        sage: gamma(3/4).n(100)
        1.2254167024651776451290983034

    The precision for the result is also deduced from the precision of the
    input. Convert the input to a higher precision explicitly if a result
    with higher precision is desired.::

        sage: t = gamma(RealField(100)(2.5)); t
        1.3293403881791370204736256125
        sage: t.prec()
        100

    The gamma function only works with input that can be coerced to the
    Symbolic Ring::

        sage: Q.<i> = NumberField(x^2+1)
        sage: gamma(i)
        Traceback (most recent call last):
        ...
        TypeError: cannot coerce arguments: no canonical coercion from Number Field in i with defining polynomial x^2 + 1 to Symbolic Ring

    .. SEEALSO::

        :class:`Function_gamma`
        """
    if not args:
        return gamma1(a, **kwds)
    if len(args) > 1:
        raise TypeError("Symbolic function gamma takes at most 2 arguments (%s given)" % (len(args) + 1))
    return gamma_inc(a, args[0], **kwds)


# We have to add the wrapper function manually to the symbol_table when we have
# two functions with different number of arguments and the same name
symbol_table['functions']['gamma'] = gamma


def _mathematica_gamma3(*args):
    r"""
    EXAMPLES::

        sage: gamma(4/3)._mathematica_().sage()       # indirect doctest, optional - mathematica
        gamma(4/3)
        sage: gamma(4/3, 1)._mathematica_().sage()    # indirect doctest, optional - mathematica
        gamma(4/3, 1)
        sage: mathematica('Gamma[4/3, 0, 1]').sage()  # indirect doctest, optional - mathematica
        gamma(4/3) - gamma(4/3, 1)
    """
    assert len(args) == 3
    return gamma_inc(args[0], args[1]) - gamma_inc(args[0], args[2])

register_symbol(_mathematica_gamma3, dict(mathematica='Gamma'), 3)


class Function_psi1(GinacFunction):
    def __init__(self):
        r"""
        The digamma function, `\psi(x)`, is the logarithmic derivative of the
        gamma function.

        .. MATH::

            \psi(x) = \frac{d}{dx} \log(\Gamma(x)) = \frac{\Gamma'(x)}{\Gamma(x)}

        EXAMPLES::

            sage: from sage.functions.gamma import psi1
            sage: psi1(x)
            psi(x)
            sage: psi1(x).derivative(x)
            psi(1, x)

        ::

            sage: psi1(3)
            -euler_gamma + 3/2

        ::

            sage: psi(.5)
            -1.96351002602142
            sage: psi(RealField(100)(.5))
            -1.9635100260214234794409763330

        TESTS::

            sage: latex(psi1(x))
            \psi\left(x\right)
            sage: loads(dumps(psi1(x)+1))
            psi(x) + 1

            sage: t = psi1(x); t
            psi(x)
            sage: t.subs(x=.2)
            -5.28903989659219
            sage: psi(x)._sympy_()
            polygamma(0, x)
            sage: psi(x)._fricas_()    # optional - fricas
            digamma(x)
        """
        GinacFunction.__init__(self, "psi", nargs=1, latex_name=r'\psi',
                               conversions=dict(mathematica='PolyGamma',
                                                maxima='psi[0]',
                                                maple='Psi',
                                                sympy='digamma',
                                                fricas='digamma'))


class Function_psi2(GinacFunction):
    def __init__(self):
        r"""
        Derivatives of the digamma function `\psi(x)`. T

        EXAMPLES::

            sage: from sage.functions.gamma import psi2
            sage: psi2(2, x)
            psi(2, x)
            sage: psi2(2, x).derivative(x)
            psi(3, x)
            sage: n = var('n')
            sage: psi2(n, x).derivative(x)
            psi(n + 1, x)

        ::

            sage: psi2(0, x)
            psi(x)
            sage: psi2(-1, x)
            log(gamma(x))
            sage: psi2(3, 1)
            1/15*pi^4

        ::

            sage: psi2(2, .5).n()
            -16.8287966442343
            sage: psi2(2, .5).n(100)
            -16.828796644234319995596334261

        TESTS::

            sage: psi2(n, x).derivative(n)
            Traceback (most recent call last):
            ...
            RuntimeError: cannot diff psi(n,x) with respect to n

            sage: latex(psi2(2,x))
            \psi\left(2, x\right)
            sage: loads(dumps(psi2(2,x)+1))
            psi(2, x) + 1
            sage: psi(2, x)._sympy_()
            polygamma(2, x)
            sage: psi(2, x)._fricas_()  # optional - fricas
            polygamma(2,x)

        Fixed conversion::

            sage: psi(2,x)._maple_init_()
            'Psi(2,x)'
        """
        GinacFunction.__init__(self, "psi", nargs=2, latex_name=r'\psi',
                               conversions=dict(mathematica='PolyGamma',
                                                sympy='polygamma',
                                                maple='Psi',
                                                giac='Psi',
                                                fricas='polygamma'))

    def _maxima_init_evaled_(self, *args):
        """
        EXAMPLES:

        These are indirect doctests for this function.::

            sage: from sage.functions.gamma import psi2
            sage: psi2(2, x)._maxima_()
            psi[2](_SAGE_VAR_x)
            sage: psi2(4, x)._maxima_()
            psi[4](_SAGE_VAR_x)
        """
        args_maxima = []
        for a in args:
            if isinstance(a, str):
                args_maxima.append(a)
            elif hasattr(a, '_maxima_init_'):
                args_maxima.append(a._maxima_init_())
            else:
                args_maxima.append(str(a))
        n, x = args_maxima
        return "psi[%s](%s)" % (n, x)

psi1 = Function_psi1()
psi2 = Function_psi2()


def psi(x, *args, **kwds):
    r"""
    The digamma function, `\psi(x)`, is the logarithmic derivative of the
    gamma function.

    .. MATH::

        \psi(x) = \frac{d}{dx} \log(\Gamma(x)) = \frac{\Gamma'(x)}{\Gamma(x)}

    We represent the `n`-th derivative of the digamma function with
    `\psi(n, x)` or `psi(n, x)`.

    EXAMPLES::

        sage: psi(x)
        psi(x)
        sage: psi(.5)
        -1.96351002602142
        sage: psi(3)
        -euler_gamma + 3/2
        sage: psi(1, 5)
        1/6*pi^2 - 205/144
        sage: psi(1, x)
        psi(1, x)
        sage: psi(1, x).derivative(x)
        psi(2, x)

    ::

        sage: psi(3, hold=True)
        psi(3)
        sage: psi(1, 5, hold=True)
        psi(1, 5)

    TESTS::

        sage: psi(2, x, 3)
        Traceback (most recent call last):
        ...
        TypeError: Symbolic function psi takes at most 2 arguments (3 given)
    """
    if not args:
        return psi1(x, **kwds)
    if len(args) > 1:
        raise TypeError("Symbolic function psi takes at most 2 arguments (%s given)" % (len(args) + 1))
    return psi2(x, args[0], **kwds)

# We have to add the wrapper function manually to the symbol_table when we have
# two functions with different number of arguments and the same name
symbol_table['functions']['psi'] = psi


def _swap_psi(a, b):
    return psi(b, a)

register_symbol(_swap_psi, {'giac': 'Psi'}, 2)


class Function_beta(GinacFunction):
    def __init__(self):
        r"""
        Return the beta function.  This is defined by

        .. MATH::

            \operatorname{B}(p,q) = \int_0^1 t^{p-1}(1-t)^{q-1} dt

        for complex or symbolic input `p` and `q`.
        Note that the order of inputs does not matter:
        `\operatorname{B}(p,q)=\operatorname{B}(q,p)`.

        GiNaC is used to compute `\operatorname{B}(p,q)`.  However, complex inputs
        are not yet handled in general.  When GiNaC raises an error on
        such inputs, we raise a NotImplementedError.

        If either input is 1, GiNaC returns the reciprocal of the
        other.  In other cases, GiNaC uses one of the following
        formulas:

        .. MATH::

            \operatorname{B}(p,q) = \frac{\Gamma(p)\Gamma(q)}{\Gamma(p+q)}

        or

        .. MATH::

            \operatorname{B}(p,q) = (-1)^q \operatorname{B}(1-p-q, q).


        For numerical inputs, GiNaC uses the formula

        .. MATH::

            \operatorname{B}(p,q) =  \exp[\log\Gamma(p)+\log\Gamma(q)-\log\Gamma(p+q)]


        INPUT:

        -  ``p`` - number or symbolic expression

        -  ``q`` - number or symbolic expression


        OUTPUT: number or symbolic expression (if input is symbolic)

        EXAMPLES::

            sage: beta(3,2)
            1/12
            sage: beta(3,1)
            1/3
            sage: beta(1/2,1/2)
            beta(1/2, 1/2)
            sage: beta(-1,1)
            -1
            sage: beta(-1/2,-1/2)
            0
            sage: ex = beta(x/2,3)
            sage: set(ex.operands()) == set([1/2*x, 3])
            True
            sage: beta(.5,.5)
            3.14159265358979
            sage: beta(1,2.0+I)
            0.400000000000000 - 0.200000000000000*I
            sage: ex = beta(3,x+I)
            sage: set(ex.operands()) == set([x+I, 3])
            True

        The result is symbolic if exact input is given::

            sage: ex = beta(2,1+5*I); ex
            beta(...
            sage: set(ex.operands()) == set([1+5*I, 2])
            True
            sage: beta(2, 2.)
            0.166666666666667
            sage: beta(I, 2.)
            -0.500000000000000 - 0.500000000000000*I
            sage: beta(2., 2)
            0.166666666666667
            sage: beta(2., I)
            -0.500000000000000 - 0.500000000000000*I

            sage: beta(x, x)._sympy_()
            beta(x, x)

        Test pickling::

            sage: loads(dumps(beta))
            beta

        Check that :trac:`15196` is fixed::

            sage: beta(-1.3,-0.4)
            -4.92909641669610
        """
        GinacFunction.__init__(self, 'beta', nargs=2,
                               latex_name=r"\operatorname{B}",
                               conversions=dict(maxima='beta',
                                                mathematica='Beta',
                                                maple='Beta',
                                                sympy='beta',
                                                fricas='Beta',
                                                giac='Beta'))

    def _method_arguments(self, x, y):
        r"""
        TESTS::

            sage: RBF(beta(sin(3),sqrt(RBF(2).add_error(1e-8)/3)))  # abs tol 6e-7
            [7.407662 +/- 6.17e-7]
        """
        return [x, y]

beta = Function_beta()
